Biomedical subjects

Nour Eddine Fahmi

Publications and source records attributed to Nour Eddine Fahmi.

5 recordsLinked to original sources

PubMed2006

Construction of modified ribosomes for incorporation of D-amino acids into proteins.

While numerous biologically active peptides contain D-amino acids, the elaboration of such species is not carried out by ribosomal synthesis. In fact, the bacterial ribosome discriminates strongly against the incorporation of D-amino acids from D-aminoacyl-tRNAs. To permit the incorporation of D-amino acids into proteins using in vitro protein-synthesizing systems, a strategy has been developed to prepare modified ribosomes containing alterations within the peptidyltransferase center and helix 89 of 23S rRNA. S-30 preparations derived from colonies shown to contain ribosomes with altered 23S rRNAs were found to exhibit enhanced tolerance for D-amino acids and to permit the elaboration of proteins containing D-amino acids at predetermined sites. Five specific amino acids in Escherichia coli dihydrofolate reductase and Photinus pyralis luciferase were replaced with D-phenylalanine and D-methionine, and the specific activities of the resulting enzymes were determined.

Acylation↗

PubMed2006

Search for cyclodextrin-based inhibitors of anthrax toxins: synthesis, structural features, and relative activities.

Recently, using structure-inspired drug design, we demonstrated that aminoalkyl derivatives of beta-cyclodextrin inhibited anthrax lethal toxin action by blocking the transmembrane pore formed by the protective antigen (PA) subunit of the toxin. In the present study, we evaluate a series of new beta-cyclodextrin derivatives with the goal of identifying potent inhibitors of anthrax toxins. Newly synthesized hepta-6-thioaminoalkyl and hepta-6-thioguanidinoalkyl derivatives of beta-cyclodextrin with alkyl spacers of various lengths were tested for the ability to inhibit cytotoxicity of lethal toxin in cells as well as to block ion conductance through PA channels reconstituted in planar bilayer lipid membranes. Most of the tested derivatives were protective against anthrax lethal toxin action at low or submicromolar concentrations. They also blocked ion conductance through PA channels at concentrations as low as 0.1 nM. The activities of the derivatives in both cell protection and channel blocking were found to depend on the length and chemical nature of the substituent groups. One of the compounds was also shown to block the edema toxin activity. It is hoped that these results will help to identify a new class of drugs for anthrax treatment, i.e., drugs that block the pathway for toxin translocation into the cytosol, the PA channel.

Animals↗

PubMed2005

Beta-cyclodextrin derivatives that inhibit anthrax lethal toxin.

Recently, we demonstrated that simultaneous blocking of bacterial growth by antibiotics and inhibition of anthrax toxin action with antibodies against protective antigen were beneficial for the treatment of anthrax. The present study examined the hypothesis that blocking the pore formed by protective antigen can inhibit the action of anthrax toxin. The potential inhibitors were chosen by a structure-based design using beta-cyclodextrin as the starting molecule. Several beta-cyclodextrin derivatives were evaluated for their ability to protect RAW 264.7 cells from the action of anthrax lethal toxin. Per-substituted aminoalkyl derivatives displayed inhibitory activity and were protective against anthrax lethal toxin action at low micromolar concentrations. These results provide the basis for a structure-based drug discovery program, with the goal of identifying new drug candidates for anthrax treatment.

Animals↗

PubMed2003

Enhanced D-amino acid incorporation into protein by modified ribosomes.

By overexpression of modified Escherichia coli 23S rRNAs from multicopy plasmids, ribosomes were prepared that contained mutations in two regions (2447-2450 and 2457-2462) of 23S rRNA. Following mutagenesis and selection, two clones with mutations in the 2447-2450 region (peptidyltransferase center) and six with mutations in the 2457-2462 region (helix 89) were characterized. The mutations were shown to exhibit a high level of homology. Cell-free protein synthesizing systems prepared from these clones were found to exhibit significantly enhanced incorporation of d-methionine and d-phenylalanine into protein. The incorporations involved positions 10, 22, and 54 of E. coli dihydrofolate reductase and positions 247 and 250 of Photinus pyralis firefly luciferase. Interestingly, some of the derived proteins containing the d-amino acids (notably DHFR analogues altered at position 10) functioned as well as those containing the respective l-amino acids, while substitution at other positions resulted in proteins having greatly diminished activity.

Amino Acids↗

PubMed2002

Total synthesis of deamido bleomycin a(2), the major catabolite of the antitumor agent bleomycin.

Metabolic inactivation of the antitumor antibiotic bleomycin is believed to be mediated exclusively via the action of bleomycin hydrolase, a cysteine proteinase that is widely distributed in nature. While the spectrum of antitumor activity exhibited by the bleomycins is believed to reflect the anatomical distribution of bleomycin hydrolase within the host, little has been done to characterize the product of the putative inactivation at a chemical or biochemical level. The present report describes the synthesis of deamidobleomycin demethyl A(2) (3) and deamido bleomycin A(2) (4), as well as the respective aglycones. These compounds were all accessible via the key intermediate N(alpha)-Boc-N(beta)-[1-amino-3(S)-(4-amino-6-carboxy-5-methylpyrimidin-2-yl)propion-3-yl]-(S)-beta-aminoalanine tert-butyl ester (16). Synthetic deamido bleomycin A(2) was shown to be identical to the product formed by treatment of bleomycin A(2) with human bleomycin hydrolase, as judged by reversed-phase HPLC analysis and (1)H NMR spectroscopy. Deamido bleomycin A(2) was found to retain significant DNA cleavage activity in DNA plasmid relaxation assays and had the same sequence selectivity of DNA cleavage as bleomycin A(2). The most significant alteration of function noted in this study was a reduction in the ability of deamido bleomycin A(2) to mediate double-strand DNA cleavage, relative to that produced by BLM A(2).

Antibiotics, Antineoplastic↗